It is known to palynologists, organic petrologists and others that the thermal history of a sedimentary rock, often referred to as its organic metamorphism or eometamorphism, can be manifested in the color of the organic matter (commonly known as kerogen) that is extracted from a specimen or core sample of the rock. The color of the kerogen, when viewed in transmitted light, provides a type of paleothermometer. It has been recognized that the present state of thermal maturity of the kerogen is a useful indicator of whether it has been heated sufficiently by or during various historical geological events to generate oil and/or natural gas. If so, the kerogen is said to be thermally mature.
During increasing thermal maturity, palynomorphs such as spores, pollen, and plant tissue fragments undergo a variety of changes in color. These substances, when found in a sedimentary rock which is considered to be immature, vary in color from colorless or chartreuse to yellow; in mature sediments they vary in color from yellow-orange and orange-brown to a light brown; in over-mature sediments they vary in color from light brown to brown; in severely altered sediments they vary in color from brown to dark brown; and in sediments that have been metamorphosed they vary in color from dark brown to black.
Sediments that contain organic matter which have generated oil are those characterized above as being thermally mature. Over-mature sediments are likely to contain organics that are in the wet or dry gas phase of hydrocarbon generation, while those classified as severely altered contain organics which may produce dry gas, hydrogen sulfide and/or carbon dioxide. Thus, a precise determination of the color of the kerogen provides a useful indicator of whether oil might be found by drilling into a certain sedimentary layer of rocks, or whether the strata is thermally too young (cold) or old (hot) to warrant the high expenses involved in exploration drilling.
Kerogen materials such as spores, pollen, plant tissue and the like are known to exhibit a variety of colors, even within the same specimen or sample. Previous color analysis systems have relied solely upon visual estimates of spore coloration and have a disadvantage in that they are highly subjective. Because of this, it is extremely difficult to define a particular color, or to erect a color scheme, that is acceptable to everyone. Therefore, different analysts will come up with different thermal maturity estimates based upon the same sample. Another commonly used analytical system uses measurements of percentage vitrinite reflection to estimate thermal maturity. However, these measurements are limited to spot readings of small diameter areas of the specimen, and the system also involves a high degree of subjectivity, particularly where anisotrophy is present. Moreover, even experts have difficulty in picking out the vitrinite in a specimen. This technique also requires that a specimen slide be exactly levelled before a meaningful measurement of reflectivity can be made. Another system described in U.S. Pat. No. 4,971,437 issued Nov. 20, 1990, employs optical spectral analysis with rapid spectral scanning which measures the wavelength of light. Two light sources are used alternatively, one providing a beam of transmitted light that passes through the rock sample held in a plate, and another beam of incidental light that causes the sample to fluoresce. A filter disk is rotated through the light beam which filters the same through a range of wave lengths, and electrical signals are generated which are representative of the intensity of the light to provide a spectral output. This method required specially designed equipment and optical systems which are very expensive to manufacture and, since amorphous debris is the organic component being measured, the analyst does not know precisely what is being measured. Moreover, the method disclosed in the '437 patent does not provide an integrated approach, as does the present invention where measurements are made of an entire spore or pollen grain.
The present invention uses the concept that color is defined by three parameters: hue, saturation and brightness. Hue denotes the particular color which our eyes perceive, for example red, green or blue or various mixtures thereof. Saturation refers to the lack of "whiteness" in a color, or more precisely, how much a color differs from neutral. On the other hand brightness, also called intensity, is a parameter that describes the perceived brilliance of color (hue) of light. For example, the sun at noon appears to have a yellow hue which is strongly saturated and extremely brilliant. However, at sunset the hue shifts to a deep blood-red color, is more highly saturated, and is less brilliant. A certain combination of these three parameters corresponds to a distinctive wavelength of visible light. The use of all of these parameters in accordance with the present invention has been found to provide much more definitive analysis than one based upon an estimated color or a particular color scheme, and even allows an analysts who may suffer from a degree of color blindness to accurately define the color of an organic constituent extracted from a rock sample.
An object of the present invention is to provide a new and improved kerogen color analysis method that obviates the above-mentioned problems and disadvantages with prior art systems and methods.
Another object of the present invention is to provide a new and improved color analysis method which virtually eliminates subjectively on the part of the analyst.
Another object of the present invention is to provide a new and improved color analysis system that is not limited to spot readings, but is based upon overall or truly integrated measurements of color values.
Still another object of the present invention is to provide a color analysis system that relies on measurement and recording of hue, saturation and brightness values which are the coordinates used in universally accepted charts which define color.